Grease Filter Efficiency Test Method - Food Service Technology ...

To determine particle collection efficiency, the large particle aerosol generator outlet was
placed on the center of the griddle and 11 in. above the griddle (with the griddle off or on)
without a filter in the hood. The OPC was used to determine the particle concentration as a
function of size of the effluent for a two minute sample period. The filter was then installed
and then the OPC sampled for another two minute sample period to determine the
downstream concentration. The collection efficiency for each particle size range is defined in
Equation 1.
This procedure was repeated to determine the average collection efficiency and uncertainty in
collection efficiency. The test protocol is given in Appendix E and the data analysis method
is given in Appendix G.
4. RESULTS
4.1 CHARACTERIZATION
4.1.1 Calibration of Griddle
The results of the griddle calibration are given in Table 4.1. The average temperature
measured for each location was found to be 375 ±5 ºF and was, therefore, within the
specification of the ASTM Standard F 1275-99 [3].
TABLE 4.1. GRIDDLE TEMPERATURES (ºF) FROM LEFT TO RIGHT
Location 1 Location 2 Location 3 Location 4 Location 5 Location 6
376 378 380 379 380 380
4.1.2 Calibration of Test Airflow Rate
The velocity profiles in the duct and the total volumetric flow rate through the duct were
obtained for a total of four flow conditions. Approximately 63 data points were taken at
each condition. As shown in Figure 4.1, the velocity profiles were found to agree well with
published results for fully developed turbulent flow [7]. The remaining velocity profiles are
given in Appendix B. The results were also used to determine the total exhaust volumetric
flow rate at each condition so that the fan-system curve could be determined (see Figure 4.2).
For a fan frequency of 24.5 Hz, the centerline velocity was found to be 1381 fpm with a total
volumetric flow rate of 1,000 CFM through the 12 in. round exhaust duct (Figure 4.3).
To obtain the correct airflow rate (1,000 CFM) when the baffles or filters were installed, the
hot-film anemometer was placed at the sampling location in the center of the duct and the fan
speed was increased until a velocity of 1381 fpm was obtained. The electrical power
frequency supplied to the fan when the baffles were used was found to be 28.0 Hz and that
for the filters was found to be 38.2 Hz. In addition, the pressure drops across the baffles and
filters were measured and found to be 0.10 in. H 2 0 and 0.41 in. H 2 0, respectively.
4.1.3 Aerosol Spatial Uniformity Tests
Before any spatial uniformity data were obtained, the aerosol concentration was measured at
the centerline of the duct with the aerosol generator located in the center of the griddle for at
least 30 minutes to check the stability of the aerosol generators. No discernable variation
with time was measured with each aerosol generator when the fluid levels in the reservoirs
were properly maintained (see Appendix C).
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